Special post: Endangered species

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Palau. Image by LuxTonnerre, licensed under Creative Commons.
Palau. Image by LuxTonnerre, licensed under Creative Commons.

Guest post written by Craig Costion

Today we use the term “endangered species” to raise awareness about species that are threatened with extinction. The use of the term ‘endangered species’, however, implies that the species has passed a strict set of criteria that assesses the number of individuals or the area occupied by individuals of that species. The International Union for Conservation of Nature (IUCN) regularly maintains and updates which species fall into this category (along with other classifications such as vulnerable and extinct in the wild) as part of its Red List.

When most people think of endangered species they think of animals such as tigers and rhinos. But did you know that to date only 5% of the world’s plants, and 1% of invertebrates, have been assessed under the IUCN Red List, compared to 100% of mammals, 100% of birds, and 94% of the world’s amphibians? These are alarming figures, especially when you consider that a recent study indicated 1 out of every 5 plants (22% of the world’s total) are at risk of extinction. We therefore urgently need more information on the vulnerability of a much broader range of species and need to be able to collect this information quickly and easily.

Fortunately help is at hand from a new method (recently published by botanist Craig Costion, archaeologist Jolie Liston, and co-authors) that combines floristic (data on which plants occur where) and archeological information. The island of Palau, in the western Pacific, was the study location used for developing this new extinction threat assessment method, which allows multiple species to be classified at the same time, even when no data on long-term changes in population size are available (normally required for IUCN assessments). The method was identical to the IUCN system, but with one important modification: it allows the inclusion of information on the history of habitat modification and destruction extending over and beyond 100 years.

Although for most tropical regions long-term population data for species is very sparse, Palau, like many other locations, has ample evidence of historic deforestation from the archaeological record. Archaeological evidence showed that over 30% of the original forest on the islands had been cut down since the arrival of humans. Thus species only found in a particular forest type that has experienced such sustained removal, in this case plants endemic to Palau’s forests, should therefore qualify as ‘threatened’. IUCN has a criterion that requires a minimum of 30% for habitat decline to classify species as ‘Vulnerable’. However, IUCN only accepts data on habitat decline that occurs over three generations or within 100 years.

In most tropical regions, forest recovery after deforestation is extremely slow, and in Palau much of the area that was previously forest is now permanent savanna or grassland. Oceanic islands and tropical areas are unique in that they commonly harbor endemic species, those that occur nowhere else on earth, which also have very small natural distributions. It may not sound like much, but a decline of 30% for a small oceanic island is a lot, especially if the island is rich in unique species. When you stop and think about it, 100 years in the life of a species that evolved over millions of years is nothing. Many species of plants, especially trees, live well over 100 years, making this 100 year restriction from IUCN a poor measure of long term population trends for plants. If a 30-50% decline in the total population size of such a species occurred over the course of a few hundred years at the hands of humans, this should be more than enough to justify global recognition of threatened status.

Currently, however, IUCN does not accept this logic, notwithstanding numerous published scientific case studies calling for modifications to IUCN’s system. Less rigid but equally credible approaches are urgently needed for areas where the population data required to meet IUCN standards are difficult to obtain.

Concerns over the methods used to classify the threat to species may seem to most people to be only remotely relevant to conservation. However, if it means that thousands of endangered species remain unnoticed and unlisted in some of the most species-rich parts of the globe then it is clearly a problem. Developing countries often rely on international grant schemes, some of which only fund conservation activities targeted towards IUCN-listed species. Thus the process of determining how a species is classified as “endangered” has a big influence on real world conservation actions.

[Featured image: Rock islands in Palau. Image by Peter Binter, in the public domain.]


Costion CM Liston J, Kitalong AH, Ida A, Lowe AJ (2012) Using the ancient past for establishing current threat in poorly inventoried regions. Biological Conservation. 147: 153–162.

Costion C, Lowe AJ (2012) Silent declines: recognising unlisted ‘endangered’ species. The Conversation 11th July.


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